Controlling communications between arrangements of computing systems improves letter of credit (“LC”) administration, speed, flexibility, and reach. The computing systems can be operated by an Applicant, Issuer, Custody Bank, and Beneficiary. LC improvements are achieved by the Applicant computing system making a LC request to the Issuer computing system, which obtains a hold on non-cash collateral and provides the hold to the Custody Bank computing system, designating the Custody Bank as both nominated person and paying agent. The Custody Bank computing system obtains a hold on the collateral, using it to immediately act on Beneficiary payment requests in kind of the collateral. Under these arrangements, the LC is capable of immediate payment and automated amendments to Stated Amounts to rebalance capacity amongst Beneficiaries of the Applicant, the LC Stated Amount and collateral values are always equal, and the LC is less susceptible to payment interference, automatic stays, and double payment.