Help with using S26MD02 Relay as a Switch
Indeed this SSR (solid state relay) will not work for your application. This device is designed to switch AC, not DC. The switching devices are TRIACs, these consist of two antiparalel Thyristors.

Thyristors and TRIACs are switching devices that only can be turned off when the current turns zero. This happens 100 or 120 times per second when using the mains AC. But not in your DC application. Probably the trigger voltage (at which the TRIACs switch on) is also significantly higher than the 5 V you're using.

So you will need to use a different device.