Bing is migrating all monthly budgets to daily budgets during the month of April, and it should be complete by April, 30.

If migrated by Bing you won't be able to add or update monthly budgets.

In the meantime, Bing suggest advertisers move their campaigns to daily budgets before a forced migration takes place.

For the forced migration, all campaign level unshared monthly budgets will be converted to a daily budget as follows:

*Monthly budget amount / 30.4 = Daily budget amount.

If the result of the division in the formula above results in a value below the minimum allowed campaign budget, it will be automatically set to the minimum value.

Delivery type will be set to “Accelerated” for daily budgets. A daily accelerated budget distributes your ad impressions across the entire month, showing your ads as quickly as appropriate each day until your daily budget is depleted.

Bing Ads Monthly Budgets to Migrate to Daily Budgets During April, 2017 [advertise.bingads.microsoft.com]