After updating to WHMCS 8.5.1, users attempting to configure the TransIP registrar module may encounter a Class not found error in certain environments:

Class 'Transip\Api\Library\TransipAPI' not found 

File path detection improperly handles environments with an underscore (_) in the WHMCS installation directory path.

A hotfix has been created for WHMCS 8.5.0 to improve the directory path handling:

https://whmcs.community/files/file/178-module-7817-class-not-found-error-in-transip/