Most probably, Welltory doesn’t have enough permissions to receive the data.
Go to Apple Health, open the Sources tab, find Welltory in the list of connected apps, and make sure it has access to all data categories (both to write and to read data). If you don’t see Welltory in the list of connected apps in Apple Health:
Go to the Welltory app.
Open the Menu.
In Sources, choose Apple Health.
Turn all categories on and tap Allow.
Sometimes, data synchronization may take a little too long.
Data from Apple Health may have not yet reached Welltory. If you see the data in Apple Health, but not in Welltory, give it 10–15 minutes to sync — this time is usually enough.
Your fitness tracker or another gadget has not yet shared its data with Apple Health.
If Apple Health gets data from another source (e.g. your fitness tracker), data transfer may have taken longer than usual. To check if this is the case:
Open the relevant section in Apple Health (e.g. Sleep or Activity → Steps).
Tap Show All Data.
See if the record you’re looking for is there.
If there’s no data in Apple Health — Welltory won’t get it either.
There has been a glitch in wi-fi / mobile internet connection, and it hasn’t been restored properly.
Try turning wi-fi and mobile data off and on again, switch from one to the other and vice versa. Usually, it helps.
And if you see incorrect/outdated data on your charts in Welltory’s My data section, you can "force" it to sync:
Go to Menu → Settings.
Tap Reload My Data.