With the freshOps Mobile Apps, you must Check-In to a Visit and also remember to Check-Out of a Visit.
If you fail to Check-Out and try to Check-In the next day to another site or visit, you will not be able to do so.
You'll either have;
NO Check-In button on iOS Apple Devices
or on Android Device
If this is the case, you need find the Visit that is still in Progress in your Visit List and Force a Checkout first.
Once you've Forced the Checkout on the In-Progress Visit, you'll now see the Check-In Buttons and be able to proceed as normal.