Sopping On line /Web VS the APP

Why prices and shipping cost are different when shopping on the web VS shopping using the APP
items are cheaper on the web but shipping more expensive, and on the APP prices are higher and shipping is less. Shouldn’t both be the same? or at least better using the App?
Here is an examples: WYZE Solar panel $19.99 on line and $22.99 on the APP
Shipping $8.99 on line and $5.99 on the App

Also why all items are not available for purchase on the APP, (example: filters for Stick vacuum) it is available on line for $ 11.99 pack of 2 but not available to select using the APP