How to avoid repeating/duplicates when multiple users use the app

[jaichith]

Hi,

How to avoid repeating/duplicates entries when multiple users use the app

Expression in Initial value to for incremental SL NO

MAX(TEST[SL NO])+1

Valid If formula: suggested by @Suvrutt_Gurjar in this post to avoid duplicates. 

Note : This expression allows to save initially but after saving , while clicking the edit button, it shows valid if error. 

ISBLANK(
FILTER(
"TEST",
([_THIS] = [SL NO])
)
- LIST([_THISROW])
)

 SL NO ( Serial Number should be sequential in nature. 

I get double entries when there are multiple users at a time. 

How to fix this issue ?