If you are utilizing a digital form for your 10dlc opt in then it should look similar to this, although there are infinite ways to do it:
1) Notice it has all the required disclaimers:
By providing your phone number, you agree to receive SMS [Use Case(s)] from [Brand Name]. Message frequency may vary. Standard Message and Data Rates may apply. Reply STOP to opt out. Reply HELP for help. We will not share mobile information with third parties for promotional or marketing purposes.
2) Sms consent checkbox is specific, explicit, and optional:
It is not buried in terms and conditions or combined with other consents like "I agree to the terms and conditions" and it is not a mandatory field.
3) The subscriber knows what to expect.
4) It is not in the image but the sms opt in check box should be unchecked by default.
If you have a non digital opt in then please look at this for guidance: