If you receive the message 'Your account has insufficient funds' when setting up a free trial via credit or debit card, this may be due to a failed verification check.
The verification check does not charge you but makes a request for a value between $1/1€ and the subscription fee to see if the funds are present in the account. If the requested funds are not available, then it will not allow you to proceed. This is in place to help prevent fraud and also abuse of the system. You will only be charged if your subscription begins after your free trial.
To solve this issue either ensure your account has funds equivalent to the subscription fee, or consider using an alternative payment method.