Using the Kwebbl SIP Trunk, please keep in mind that there is no number normalization at the Kwebbl side as you are used to with a SIP device. This means that you should adjust the number format to E.164 (eg. 31201234567) in your own PBX.
You can ty calling to a number in E.164 format to check if outbound calls are possible. If so, then you should check the settings in your PBX to adjust an outgoing call starting with 0 will be transferred into eg. 31.
Besides the CLI settings please check the PBX for the P-Asserted Identity settings. Besides the FROM header, the CallerID should always be set in the P-Asserted-Identity header in the PBX. In some cases the Remote-Party-ID header might serve as a viable but unsupported alternative. Calls without the correct CallerID headers might be ignored.
Besides the From header, the caller ID should always be set in the P-Asserted-Identity header. In some cases the Remote-Party-Id header might serve as a viable but unsupported alternative. Calls without correct Caller ID headers might be ignored.