This seems may be you are involving the MTP resources while calling through either Gateway or Gatekeeper Trunk where the option 'Media Termination Point Required' is checked. Sometime the mentioned devices are already using the registered MTPs with CUCM and there is more demand of MTP for any reason so it's giving you such message 'no MTP resources available'.
If your MTP are already unused but you are still getting the message reset the MTPs and also restart the 'IP Voice Media Streaming Service' from serviceability page.
If you actually need more MTP then you can add some more Hardware MTP from IOS gateways with additional sessions you need.
This means there is some mismatch on your configuration.
Can you please post your dspfarm profile config from your gateway for transcoder? Also, can you make sure you have added your hardware transcoders as 'Cisco IOS Enhanced Media Termination Point' with correct Device Name?
'codec pass-thru' is typically used for passing T.38 capabilities through an MTP/transcoder.
What codecs was it trying to nail up on each side of the transcoder when the error would occur? If one of the legs wasn't g711, it will fail. Best practice is to put your MTPs in their own MRG higher in the MRGL list from the MRG with the transcoder. That way, when we just need a normal MTP, a transcoder doesn't get invoked (since unless you have universal transcoder support, xcoder allocation will fail on calls that aren't g711 on at least one leg).
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