In case you want to allow your affiliate to choose their own coupon code, you can ask them to fill in their preferred coupon code right on the registration form. You can then assign a proper coupon code to the affiliate. To get this done, there are two options for you:
You can see all information that your members filled in by going to Affiliates & coupons > Affiliates > click the View button. Since you've acknowledged the affiliate's preferred coupon code, you could manually create and assign a coupon for each affiliate by following the instruction about Tracking by coupon.
The manual tasks could be time-consuming especially when you have too many affiliates. Our recommendation would be to let the work done automatically.
Basically, there is a simple step you need to do to get it to work: setting up an auto-generated coupon.
Go to Settings > General > switch on Auto-generate coupon > click Setup coupon.
Create a sample coupon which has the rule you want future auto-generate coupons to follow.
Coupon Name's Style > select Affiliates select while registering
Enter a short description for the coupon > click Add.
After activating the feature, the Coupon field will be put on your registration form and marked as required. So your affiliate must enter their preferred coupon upon signing up.
Also, if your affiliate chooses a coupon which already exists in your shop, there would be a notification for them to change to another coupon.