I'm using Magento 2.3.1 with Vnecoms multi-vendor extension and I'm trying to pay with PayPal-Express – mode sale & sandbox.
I can log in in Paypal & it redirects me to the page to choose the shipment.

Arrived there exception.log & debug.log give me:

main.CRITICAL: The "3000000008" order ID is incorrect. Verify the ID
and try again. {"exception":"[object] (Exception(code: 0): The
\"3000000008\" order ID is incorrect. Verify the ID and try again. at
/var/www/html/vendor/magento/module-paypal/Model/Ipn.php:143)"} []

This doesn't happen in Authorization mode for some reason.

payment.log looks like this:

[2019-04-09 08:04:25] main.DEBUG: array (
  'url' => 'https://api-3t.sandbox.paypal.com/nvp',
  'DoExpressCheckoutPayment' =>
  array (
    'TOKEN' => 'EC-1Y3185946J772174S',
    'PAYERID' => 'D2Q6ZYP2U59WA',
    'PAYMENTACTION' => 'Sale',
    'AMT' => '16.89',
    'CURRENCYCODE' => 'EUR',
    'BUTTONSOURCE' => 'Magento_Cart_Community',
    'NOTIFYURL' => 'https://shop.2mazing.com/paypal/ipn/',
    'RETURNFMFDETAILS' => 1,
    'SHIPPINGAMT' => '0.90',
    'ITEMAMT' => '15.99',
    'TAXAMT' => '0.00',
    'L_NUMBER0' => NULL,
    'L_NAME0' => 'Autositzauflage -Gray',
    'L_QTY0' => 1,
    'L_AMT0' => '15.99',
    'L_NUMBER1' => 'store_credit',
    'L_NAME1' => 'Shop-Guthaben',
    'L_QTY1' => 1,
    'L_AMT1' => '0.00',
    'BUSINESS' => NULL,
    'EMAIL' => 'kauf@2mazing.com',
    'FIRSTNAME' => 'Simon Schmidt',
    'LASTNAME' => NULL,
    'MIDDLENAME' => NULL,
    'SALUTATION' => NULL,
    'SUFFIX' => NULL,
    'COUNTRYCODE' => 'DE',
    'STATE' => 'Empty',
    'CITY' => 'Freiburg',
    'STREET' => 'ESpachstr. 1',
    'ZIP' => '79111',
    'PHONENUM' => NULL,
    'SHIPTOCOUNTRYCODE' => 'DE',
    'SHIPTOSTATE' => 'Empty',
    'SHIPTOCITY' => 'Freiburg',
    'SHIPTOSTREET' => 'ESpachstr. 1',
    'SHIPTOZIP' => '79111',
    'SHIPTOPHONENUM' => NULL,
    'SHIPTOSTREET2' => '',
    'STREET2' => '',
    'SHIPTONAME' => 'Simon Schmidt ',
    'ADDROVERRIDE' => 1,
    'METHOD' => 'DoExpressCheckoutPayment',
    'VERSION' => '72.0',
    'USER' => '****',
    'PWD' => '****',
    'SIGNATURE' => '****',
  ),
  'response' =>
  array (
    'TOKEN' => 'EC-1Y3185946J772174S',
    'SUCCESSPAGEREDIRECTREQUESTED' => 'false',
    'TIMESTAMP' => '2019-04-09T08:04:25Z',
    'CORRELATIONID' => '23b2aead9b48f',
    'ACK' => 'Success',
    'VERSION' => '72.0',
    'BUILD' => '52346509',
    'TRANSACTIONID' => '70R244159E137901D',
    'TRANSACTIONTYPE' => 'cart',
    'PAYMENTTYPE' => 'instant',
    'ORDERTIME' => '2019-04-09T08:04:24Z',
    'AMT' => '16.89',
    'FEEAMT' => '0.67',
    'TAXAMT' => '0.00',
    'CURRENCYCODE' => 'EUR',
    'PAYMENTSTATUS' => 'Pending',
    'PENDINGREASON' => 'paymentreview',
    'REASONCODE' => 'None',
    'PROTECTIONELIGIBILITY' => 'Ineligible',
    'INSURANCEOPTIONSELECTED' => 'false',
    'SHIPPINGOPTIONISDEFAULT' => 'false',
    'PAYMENTINFO_0_TRANSACTIONID' => '70R244159E137901D',
    'PAYMENTINFO_0_TRANSACTIONTYPE' => 'cart',
    'PAYMENTINFO_0_PAYMENTTYPE' => 'instant',
    'PAYMENTINFO_0_ORDERTIME' => '2019-04-09T08:04:24Z',
    'PAYMENTINFO_0_AMT' => '16.89',
    'PAYMENTINFO_0_FEEAMT' => '0.67',
    'PAYMENTINFO_0_TAXAMT' => '0.00',
    'PAYMENTINFO_0_CURRENCYCODE' => 'EUR',
    'PAYMENTINFO_0_PAYMENTSTATUS' => 'Pending',
    'PAYMENTINFO_0_PENDINGREASON' => 'paymentreview',
    'PAYMENTINFO_0_REASONCODE' => 'None',
    'PAYMENTINFO_0_PROTECTIONELIGIBILITY' => 'Ineligible',
    'PAYMENTINFO_0_PROTECTIONELIGIBILITYTYPE' => 'None',
    'PAYMENTINFO_0_SELLERPAYPALACCOUNTID' => 'merchant@2mazing.com',
    'PAYMENTINFO_0_SECUREMERCHANTACCOUNTID' => 'TCH52AZ5XS3HG',
    'PAYMENTINFO_0_ERRORCODE' => '0',
    'PAYMENTINFO_0_ACK' => 'Success',
  ),
) [] []

If I try to pay PHP gives me the following error:

Fatal error: Uncaught TypeError: Argument 1 passed to
Magento\Sales\Model\Order\Address\Renderer::format() must be an
instance of Magento\Sales\Model\Order\Address, null given, called in
/var/www/html/vendor/vnecoms/module-vendors-sales/Model/Order/Email/Sender.php
on line 148 and defined in
/var/www/html/vendor/magento/module-sales/Model/Order/Address/Renderer.php:51
Stack trace: #0
/var/www/html/vendor/vnecoms/module-vendors-sales/Model/Order/Email/Sender.php(148):
Magento\Sales\Model\Order\Address\Renderer->format(NULL, 'html') #1
/var/www/html/vendor/vnecoms/module-vendors-sales/Model/Order/Email/Sender/OrderSender.php(137):
Vnecoms\VendorsSales\Model\Order\Email\Sender->getFormattedShippingAddress(Object(Magento\Sales\Model\Order\Interceptor))

2 /var/www/html/vendor/vnecoms/module-vendors-sales/Model/Order/Email/Sender.php(82):

Vnecoms\VendorsSales\Model\Order\Email\Sender\OrderSender->prepareTemplate(Object(Vnecoms\VendorsSales\Model\Order))

3 /var/www/html/vendor/vnecoms/module-vendors-sales/Model/Order/Email/Sen

in
/var/www/html/vendor/magento/module-sales/Model/Order/Address/Renderer.php
on line 51

These errors are only occurring in Paypal Sale mode.

Also if I don't allow multiple payments per invoice ID in Paypal, I get the PayPal gateway rejected request – duplicate invoice issue.

Any ideas on how to solve this?