When VLOOKUP fails, it is almost always one of these causes.
1. Extra spaces
"A101 " is not the same as "A101". Clean both columns with TRIM.
2. Numbers stored as text
A number on one side and text on the other will not match. Convert with VALUE, or Text to Columns, or multiply by 1.
3. Lookup value not in the first column
VLOOKUP only searches the first column of the table. Move the column, or use XLOOKUP or INDEX and MATCH.
4. Wrong column number
Count columns from the first column of the table array, not from column A of the sheet.
5. Approximate match by mistake
If you leave out the last argument, VLOOKUP assumes TRUE and may return a wrong value. Add FALSE for an exact match.
6. Table range not locked
When copying down, the table moves and some rows fail. Lock it: $A$2:$C$100 (press F4).
7. Real mismatch
Check for different spellings, hidden characters or a missing item in the table.
8. Calculation set to manual
Go to Formulas, Calculation Options and choose Automatic.
Show a clean message
=IFNA(VLOOKUP(F2, A2:C100, 3, FALSE), "Not found")