I’ve just added the Paypal payment gateway to an EE CartThrob site running the following software versions: EE 5.3.0 CT 4.6.2
When placing orders using Paypal, the buyer was getting a “13113” error code from Paypal, saying their payment couldn’t not be processed. Paypal state that this error code is caused by a security problem with the Buyer’s credentials.
However - to let everyone know - I’ve found that updating the CT version to v5+ solves this issue.
I suspect with CT 5+ being made to use the Omnipay3 platform (which has latest security protocols) Paypal is happy with this setup.
Hope this helps.