Spendence.club is a mostly empty website created to carry out a browser-based tactic specifically. Unsuspecting visitors who land on it will be shown various fake error messages and alerts that all have the same goal - to trick the user into clicking the 'Allow' button. No matter the specific text of the message, it has nothing to do with the actual consequences of following the instructions. For example, Spendence.club may attempt to mimic a legitimate captcha check by stating that users have to click 'Allow' to confirm that they are not robots or they have to click 'Allow' to close the page. Still, instead, users will be granting the unsafe website all the browser permissions it needs to start delivering unsolicited advertisements to their devices.
The advertisements could redirect to other suspicious websites, promote dubious online game sites, or attempt to trick users into downloading fake software updates. The number of displayed advertisements could start to interfere with the normal use of the device, and simply closing the affected browser will do little to mitigate the situation.
To stop Spendence.club from disrupting your browsing experience, just open the 'Settings' menu of the browser, navigate to the 'Permissions' section, and revoke anything that is associated with this dubious website.