Where can I find my error. Reject Code:IND-511-01, I need to fix the married filing separated. We are legally not married but not divorced. Can you help me fix it

are you in a common law marriage recognized by the state?

if yes,  generally, the IRS recognizes common law marriages as legal marriages if you’re in a state that recognizes common law marriages. If you’re in a state that doesn’t recognize common law marriages, the IRS generally won’t recognize you as married. 

if you're in a recognized common law marriage, your choices are a joint return or married filing separately.

so if the other party filed MFS you must do the same unless both of you can agree to refile as a joint return.

both parties must use the same method - either itemizing deductions or using the standard deduction.

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if you are not in a recognized common law marriage, the other party misfiled by using the filing status married filing separately. They will have to amend their return to either single or head of household if they have a qualifying dependent.   Your filing status would also be either single or head of household if you have a qualifying dependent.  you can try changing but the other filing as MFS may block you from e-filing so your return will have to be printed signed and mailed.

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here are the rules for head of household - note only one of you can claim a dependent but if there are multiple dependents you can split them any way you agree to

Head of household

1) Did you have any dependents? – if no you cannot file as HOH.
2) If yes, was the dependent claimable solely because of a multiple support agreement - if yes you cannot file as HOH, if no was the dependent legally related to the taxpayer by blood - if no you cannot file as HOH.
3) Do you qualify as a surviving spouse because your spouse died in the preceding 2 years and you maintain a home for a child whom you can claim as a dependent whether you do or not - you can not file as HOH but as surviving spouse.
4) Were you a nonresident alien at any time during the year - if yes you cannot file as HOH.
5) If you were not legally wed on the last day of the year, see A, if you were then 6.
6) Were you legally wed to a non-resident alien at any time in 2023, if yes see A, if not then 7.
7) If legally married, were you legally separated at the end of 2023 under a decree of separate maintenance, if yes see A, if not then 8.
😎 Did you maintain separate living quarters from your spouse, if legally wed, for the last 6 months of 2022, if yes see A, if no you cannot file as HOH.

A. then was the dependent a married child of the taxpayer? if yes, will the dependent child file a joint return with their spouse? if yes you cannot file as HOH. If the dependent child was not married or if married will not file a joint return with their spouse then did the legally related dependent use the taxpayer’s household, for which the taxpayer paid at least ½ the cost, as their principal place of abode for more than ½ the year – then you can file as HOH.