Failed to get method for command zatca_erpgulf.zatca_erpgulf.sign_invoice.create_csr with module

I’m getting this error message after clicking on the “Create CSR” button.

Steps I’ve performed:
I’ve locally setup a frappe bench and installed erpnext version 15 and then installed the zatca_erpgulf app (bench get-app GitHub - ERPGulf/zatca_erpgulf: Implementation of Zatca Phase-2 E-Invoicing - for FrappeCLoud)

Since I just wanted to test it, I entered the OTP from the Sandbox Integration Page (since, I’m a developer without an actual account on the official zatca portal)
Regardless, it gave me this non-otp related error.

Can you please provide some guidance to help me out.

Error Screenshot:

Thanks