Pick Tabby at checkout and the total is shown as 4 equal monthly payments. On your first use you sign up using your mobile number, email address and Saudi ID, then pay the first instalment immediately; the remaining ones are taken automatically from the same card.
The number of instalments and their amount are fixed, and everything happens on the adidas site, so the Tabby app isn’t needed. Tabby can be used on every product, and returns are handled under the usual return policy.
The help center also lists PayPal, American Express, Visa and Mastercard as payment options.
Source: adidas Saudi Arabia: FAQ