Maybe this will help someone. I was able to successfully connect my Meridian Explorer² USB DAC to my OnePlus 3T using this Type-C OTG cable:
https://oneplus.net/ca_en/oneplus-type-c-otg-cable
At first it would not power up the DAC, so I went into Developer Options in Settings and set Select USB Configuration to Audio Source. Reconnected the DAC and it launched USB Audio Player. Works great with local files on my phone, network files from my NAS server as well as TIDAL (including MQA),
https://oneplus.net/ca_en/oneplus-type-c-otg-cable
At first it would not power up the DAC, so I went into Developer Options in Settings and set Select USB Configuration to Audio Source. Reconnected the DAC and it launched USB Audio Player. Works great with local files on my phone, network files from my NAS server as well as TIDAL (including MQA),