"Host must be a string" error

[bporcelli]

Due to Guzzle issue #2458, some merchants with older versions of PHP intl/ICU installed on their system are getting a "host must be a string" error during checkout.

Proposed solution

Disable IDN conversion by passing idn_conversion => false to the Guzzle client constructor. We only ever make requests to taxcloud.com, which is not an IDN, so this should not cause any issues.