Which formats may be used to add a custom campaign parameter to a URL?

The correct formats for custom campaign parameters use an equals sign (=) to assign a value to the parameter and do not include spaces around the equals sign. Additionally, spaces within the parameter value itself are not allowed; instead, hyphens (-) or underscores () should be used to separate words for readability. The incorrect options include spaces around the equals sign (?utm campaign = fallsale and ?utmcampaign = fall sale), which breaks the URL structure. The option ?utmcampaign = fall sale also incorrectly uses a space within the parameter value, which would not be properly interpreted by Google Analytics.