An MT4 custom indicator cannot be run directly in MT5. This also applies to an MT4 Expert Advisor (EA). A similarly named MT5 tool may be available, but it must be a version built for MT5; changing the file name does not convert it.
Check which files you have
MT4: .mq4 is source code and .ex4 is the compiled program. MT5: .mq5 is source code and .ex5 is the compiled program. Source code is what a developer edits; compilation creates a program for the corresponding platform.
Renaming .ex4 to .ex5, copying an MT4 file into an MT5 folder or opening it in an editor does not make it an MT5 program. If you only have .ex4, you do not have the editable source code simply because the indicator runs in MT4.
Moving source code to MQL5 can require changes to calculations, data access, indicator buffers and event handling. Successful compilation is one stage; it does not prove identical output or correct trading behaviour.
Choose a suitable option
Obtain an MT5 version from the original developer or a source you trust. Confirm that it is for MT5, that the version and required supporting files are correct, and that any licence permits your intended use. A matching name or screenshot is not enough.
Keep using the MT4 version in MT4 if it meets your needs. The two terminals are separate; select the matching FXT trading account and server in each. Installing MT5 does not move an MT4 indicator, account or open position into MT5.
If you own or are authorised to modify the source, ask a qualified developer to adapt and test it for MQL5. Retain the original files and agreed calculation settings so you can compare the result. Conversion is not a simple file-extension change.
Check the replacement before using it
Compare the same instrument, timeframe, input settings and available price history. Check plotted values, signals and alerts rather than assuming matching names mean matching calculations. For an EA, test its trade requests on a Demo account before considering use on a live account.
If the tool fails to load or behaves differently, record the platform/version, program name, inputs and relevant error text for investigation. Avoid sending passwords or one-time codes. An installed or compiled tool does not guarantee execution, accuracy or profit.
Desktop, Web Trader and App are different environments
These file formats concern desktop MetaTrader programs. Do not assume they can be imported into Web Trader or FXTRADING.com App; use the chart tools actually offered by that interface. EAs cannot be installed or run in FXTRADING.com App.