@CorrectiveBody sorry to hear that you're experiencing that error. In most cases like this our troubleshooting guide does the trick to correct these. Give those a shot and if you're still seeing the error afterward please let me know in a direct message and I can get some further information from you. In the meantime are you able to send the customer a regular message suggesting another day and time?
@CorrectiveBody It sounds like the customer found your public profile and decided that they were interested in your information enough to send you a message or booking suggestion. In these cases, you'll pay when you respond to the customer. If you'd like to respond with a different day and time you can do so, or if the original day and time won't work for you, then you can feel free to pass and we'll suggest other pros for the customer.