If you didn’t know, in sha Allah it is valid

I missed the main jama’ah today so someone told me to lead the 2nd jama’ah.Unfortunately, another jama’ah was going on but I didn’t notice it.Here in Oman,Omanis pray sunnah in jama’ah immediately after fard with iqama.I presume it was sunnah as when I entered the mosque I didn’t see them standing for jama’ah).Someone was telling me when I already started.Is our prayer valid.

Prayer | March 9, 2017 6:05 am
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I shared the fatwa of islamqa.info on missed prayers on my Insta page and a few sisters started messaging me things like: Some alims recommend that you pray qadah whether you missed a prayer intentionally or unintentionally. And when someone has been given that advice it makes it confusing for them if they get another advice stating that they shouldn’t pray if missed intentionally. Help please?
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Shaikh, during traveling while praying in Jamah,I follow the Imam for farz salah but pray qhasr when alone. Also I don’t offer anyother Sunnah.However,if I have time before farz jamah,do I pray Tahiyatul Masjid before I sit ? What about 2 rakah Sunnah before Fajr Farz salah ?