The CallApp Premium version without ads is available for a monthly payment (‘Go Pro – Ad-Free’ –> ‘Buy CallApp’) or for a one-time payment (‘Go Pro – Ad Free’ –> ‘For one-time payment’).
The purchase of the premium version is done through Google Play.
They support a variety of payment methods in different countries.
We suggest you check this link to see what methods (other than credit card) are accepted in your country:
If you have further questions don’t hesitate to contact us at firstname.lastname@example.org