“Sachchā Sumatināth” actually refers to Bhagwan Sumatinath, the 5th Tirthankar of our current time-cycle.

Some key points in very simple words:

• He is the 5th Tirthankar (after Abhinandannath, before Padmaprabhu).
• His symbol (lāñchhan) is a hans / goose.
• He was born in Ayodhya in the Ikshvaku vansh.
• He taught the same main Jain principles:

ahimsā (non‑violence), satya (truth), aparigraha (non‑attachment), etc.

If by “Sacha Sumatinath” you meant a particular derāsar / Gruh Jinalay name, then it is just a respectful temple name for Sumatinath Bhagwan, often written as “Shri Sacha Sumatinath Bhagwan Jinalay / Derasar”. You can see an example here and here .