According to Bandwidth.com user guides, in the North American Numbering Plan area, they accept 10 or 11 digits as in NXXNXXXXXX or 1NXXNXXXXXX. For international calling, they require the ‘+’, country code and number. The leading +1NXXNXXXXXX may also be allowable for calling within the NANP. If this is not working for you, double-check your outbound route patterns in FreePBX or contact the carrier’s support group since carrier documentation is not always current.
See: https://support.bandwidth.com/hc/en-us/articles/204138866-Outbound-calling-integration-guide
A user in this thread says they had to contact Bandwidth.com to allow 10-digit dialing. It is quite possible that they have not properly set up your account for outbound calling patterns you expect.