Good day @suisser,
Thank you for posting to the PayPal community.
This should be an issue with your third party API permissions setup with the “Shopify” Partner.
I would suggest to please contact your third party platform(Shopify) who can able to help you onboard/link your LIVE account.
Here are instruction on how to manually the merchant can view any partner consent they have given:
1. Log into your PayPal account
2. Hover over your account name in the upper-right corner
3. Click "Account Settings"
4. On the left under "Products and Settings", click "Website Payments"
5. Click "Update" next to "API Access"
6. Under "Pre-built Payment Solution", click "Manage API Permission"
7. Click the checkbox next to SignUp
8. Click "Yes, revoke"
9. Reattempt to integrate onboard.
Merchants can manually grant permission to a third party software to access specific information in your PayPal account and perform PayPal API operations on your behalf.
Login PayPal.com >> Settings >> Account Settings >> Website payments >> API Access >> Pre-built payment solution >> Grant API permission >> contact your "Third party software (Shopify)" for Third Party Permission Username >> enter the username.
Direct link - https://www.paypal.com/cgi-bin/webscr?cmd=_profile-api-grant-authorization
If your still facing any issues, please create a MTS ticket via - https://www.paypal-support.com/s/?language=en_US with the detail information and error details.
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