Unlock code

https://www.t-mobile.com/responsibility/consumer-info/policies/sim-unlock-policy

specifically…

Unlock eligibility requirements

We unlock mobile devices that meet the following eligibility criteria free of charge.

Device eligibility is determined as follows:

• The device must be sold by T-Mobile.
• The device must not be reported as lost, stolen or blocked.
• The account associated with the device must be in good standing.
• The device must also satisfy all the Postpaid or Prepaid unlocking requirements outlined below.

Unlock eligibility for mobile devices on Postpaid plans

• The device must have been active on the T‑Mobile network for at least 40 days on the requesting line.
• If the device was financed or leased through T‑Mobile then all payments must be satisfied and the device must be paid in full.
• If the device is associated with a canceled account, then the account balance must be zero.
• T‑Mobile may request proof of purchase or additional information in its discretion and certain other exceptions may apply.

Unlock eligibility for mobile devices on Prepaid plans

• At least  365 days  must have passed since the device was activated on the T Mobile network.
• If the device was activated less than 365 days ago, then the   Prepaid account associated with the device must have had more than $100 in refills during that period for each line active on the account.  In   addition, more than 14 days must have passed since the device was purchased.
• No more than 2 mobile device unlocks have been complete per line of service in the last 12 months.
• T‑Mobile may request proof of purchase or additional information in its discretion and certain other exceptions may apply.

Como puedo desbloquear mi teléfono, cuando le pongo en desbloquear permanente me aparece una ventana que dice, error en código 6 (146) , que puedo hacer?

Mon telephone me demande un code de deverrouillage reseau,  je suis allée dans le paramettre mais cela ne resoudre pas

Are you using the Tmobile USA network and is it a Tmobile USA branded phone?

Even though T-Mobile owns Metro you need to contact Metro to fix this issue.

I'd ordered my S23 Ultra 512GB. Once I got it in the mail. I'd paid it off. Why the 40 days wait after I'd paid it all in full? Shouldn't I have all rights to my phone since it's all paid off?

pretty much the same no matter which carrier you go with. some you must do more than 40 days before you can request the unlock..

That sounds like it is due to the device still being on an EIP.  The device must be comoletely oaid iff before being eligible for a permanent SIM unlock.  

https://www.t-mobile.com/responsibility/consumer-info/policies/sim-unlock-policy

You can reach out to the T-Force Team though through Facebook or Twitter to see if an exception can be made as long as you meet all of the other SIM Unlock Policy requirements.