You are quite correct; they have used the wrong provisions under the Immigration Rules to process your husband's application. The correct provisions are under paragraph 281 which can be found be clicking the link below:
Your husband should lodge the appeal within the 28 day period. It can be lodged at British High Commission or by fax to Tribunal in UK. The deadline should not be missed under any circumstances. However, I would also urge him to write to British High Commission (obtain contact details from their website: http://ukinpakistan.fco.gov.uk/en), point out the error and ask them to review the decision (I believe that your husband must lodge any review request immediately and certainly within 20 days of receiving it).
If review takes place and is in your husband's favour, the appeal can simply be withdrawn. If the review does not take place, your husband's appeal will proceed to a paper or oral hearing in the UK.
The type of hearing has to be chosen from the Appeal Notice. Evidence will need to be submitted when directed by the Tribunal by your husband that he satisfied the relevant provisions of paragraph 281 at the time of the refusal.
Evidence will depend on your individual circumstances and so any suggested list of supporting documents cannot be considered exhaustive. Usually evidence includes: sponsor's undertaking as to maintenance and accomodation; evidence of funds (minimum 3mths bank/savings statements and wage slips for sponsor); property assessment report highlighting that adequate accomodation is available for your husband in UK (no overcrowding provisions of Housing Act 1985 must be followed); decree absolutes if applicable, sponsor's legal status in UK (copy British passport or other passport with indefinite leave to remain stamp endorsement); evidence that both of you are at least 21 yrs old; evidence that your marriage is genuine and subsisting (marriage certificate, photographs, letters etc).
Hope that helps. Kind regards
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